As you might already know, the key is communication. As you described, nobody took the chance to say anything and that lead to frustration. Therefore it is so important to have an after talk. Try to think about your emotions and thoughts you had during the act to prepare for this, but also consider the general things in your relationship. Often the problem lies a bit deeper and might not even be connected to sexual things.

Try to be open and understanding, first think about what you could have done wrong. Formulate your sentences like this, send "I-messages" not "You-messages". Take your partners thoughts seriouelsy. Create an atmosphere where both of you feel they can be honest.

You mention "poor health" could be a factor. This has two components that are important for sex, one is fitness, the other one is attractiveness. Have you considered your wife has a point here? When married people often change, eat more, do less sports, they gain weight etc. This can happen without yourself realizing. Be honest with yourself, make a check and see if you are still happy with your fitness and body form. If yo are not, who knows, maybe your wife is ready to support you somehow? You would wonder how sexy it can be when someone just says "I was working out for 1 hour straight today" - you don't even have to wait for results.

You are starting to reflect upon yourself, and that's a great thing! Good luck for you!